System and method for supporting higher-layer protocol messaging in an in-band modem

ABSTRACT

Acknowledging a source terminal data message from a destination terminal in an in-band communication system is disclosed. A first synchronization sequence followed by a low layer acknowledgement message and a second synchronization sequence followed by a high layer acknowledgement message is transmitted.

RELATED APPLICATIONS I. Claim of Priority

A claim of priority is made to the following U.S. ProvisionalApplications:

No. 61/187,393 entitled “SYSTEM AND METHOD FOR SUPPORTING HIGHER-LAYERPROTOCOL MESSAGING IN AN IN-BAND MODEM” filed Jun. 16, 2009, andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

No. 61/325,732 entitled “SYSTEM AND METHOD FOR ENHANCING THESYNCHRONIZATION SIGNAL IN AN IN-BAND MODEM” filed Apr. 19, 2010, andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

No. 61/327,004 entitled “SYSTEM AND METHOD FOR SUPPORTING HIGHER-LAYERPROTOCOL MESSAGING IN AN IN-BAND MODEM” filed Apr. 22, 2010, andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

II. Reference to Co-Pending Applications for Patent

Related co-pending U.S. patent applications include:

Ser. No. 12/477,544 entitled “SYSTEM AND METHOD OF AN IN-BAND MODEM FORDATA COMMUNICATIONS OVER DIGITAL WIRELESS COMMUNICATION NETWORKS” filedJun. 3, 2009, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

Ser. No. 12/477,561 entitled “SYSTEM AND METHOD OF AN IN-BAND MODEM FORDATA COMMUNICATIONS OVER DIGITAL WIRELESS COMMUNICATION NETWORKS” filedJun. 3, 2009, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

Ser. No. 12/477,574 entitled “SYSTEM AND METHOD OF AN IN-BAND MODEM FORDATA COMMUNICATIONS OVER DIGITAL WIRELESS COMMUNICATION NETWORKS” filedJun. 3, 2009, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

Ser. No. 12/477,590 entitled “SYSTEM AND METHOD OF AN IN-BAND MODEM FORDATA COMMUNICATIONS OVER DIGITAL WIRELESS COMMUNICATION NETWORKS” filedJun. 3, 2009, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

Ser. No. 12/477,608 entitled “SYSTEM AND METHOD OF AN IN-BAND MODEM FORDATA COMMUNICATIONS OVER DIGITAL WIRELESS COMMUNICATION NETWORKS” filedJun. 3, 2009, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

Ser. No. 12/477,626 entitled “SYSTEM AND METHOD OF AN IN-BAND MODEM FORDATA COMMUNICATIONS OVER DIGITAL WIRELESS COMMUNICATION NETWORKS” filedJun. 3, 2009, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

BACKGROUND

I. Field

The present disclosure generally relates to data transmission over aspeech channel. More specifically, the disclosure relates to a systemand method for supporting higher layer protocol messaging through aspeech codec (in-band) in a communication network.

II. Description of Related Art

Transmission of speech has been a mainstay in communications systemssince the advent of the fixed line telephone and wireless radio.Advances in communications systems research and design have moved theindustry toward digital based systems. One benefit of a digitalcommunication system is the ability to reduce required transmissionbandwidth by implementing compression on the data to be transferred. Asa result, much research and development has gone into compressiontechniques, especially in the area of speech coding. A common speechcompression apparatus is a “vocoder” and is also interchangeablyreferred to as a “speech codec” or “speech coder.” The vocoder receivesdigitized speech samples and produces collections of data bits known as“speech packets”. Several standardized vocoding algorithms exist insupport of the different digital communication systems which requirespeech communication, and in fact speech support is a minimum andessential requirement in most communication systems today. The 3rdGeneration Partnership Project 2 (3GPP2) is an example standardizationorganization which specifies the IS-95, CDMA2000 1xRTT (1x RadioTransmission Technology), CDMA2000 EV-DO (Evolution-Data Optimized), andCDMA2000 EV-DV (Evolution-Data/Voice) communication systems. The 3rdGeneration Partnership Project (3GPP) is another example standardizationorganization which specifies the GSM (Global System for MobileCommunications), UMTS (Universal Mobile Telecommunications System),HSDPA (High-Speed Downlink Packet Access), HSUPA (High-Speed UplinkPacket Access), HSPA+ (High-Speed Packet Access Evolution), and LTE(Long Term Evolution). The VoIP (Voice over Internet Protocol) is anexample protocol used in the communication systems defined in 3GPP and3GPP2, as well as others. Examples of vocoders employed in suchcommunication systems and protocols include ITU-T G.729 (InternationalTelecommunications Union), AMR (Adaptive Multi-rate Speech Codec), andEVRC (Enhanced Variable Rate Codec Speech Service Options 3, 68, 70).

Information sharing is a primary goal of today's communication systemsin support of the demand for instant and ubiquitous connectivity. Usersof today's communication systems transfer speech, video, text messages,and other data to stay connected. New applications being developed tendto outpace the evolution of the networks and may require upgrades to thecommunication system modulation schemes and protocols. In some remotegeographical areas only speech services may be available due to a lackof infrastructure support for advanced data services in the system.Alternatively, users may choose to only enable speech services on theircommunications device due to economic reasons. In some countries, publicservices support is mandated in the communication network, such asEmergency 911 (E911) or eCall. In these emergency application examples,fast data transfer is a priority but not always realistic especiallywhen advanced data services are not available at the user terminal.Previous techniques have provided solutions to transmit data through aspeech codec, but these solutions are only able to support low data ratetransfers due to the coding inefficiencies incurred when trying toencode a non-speech signal with a vocoder.

Transmitting data through a speech codec is commonly referred to astransmitting data “in-band”, wherein the data is incorporated into oneor more speech packets output from the speech codec. Several techniquesuse audio tones at predetermined frequencies within the speech frequencyband to represent the data. Using predetermined frequency tones totransfer data through speech codecs, especially at higher data rates, isunreliable due to the vocoders employed in the systems. The vocoders aredesigned to model speech signals using a limited number of parameters.The limited parameters are insufficient to effectively model the tonesignals. The ability of the vocoders to model the tones is furtherdegraded when attempting to increase the transmission data rate bychanging the tones quickly. This affects the detection accuracy andresults in the need to add complex schemes to minimize the data errorswhich in turn further reduces the overall data rate of the communicationsystem. Therefore, a need arises to efficiently and effectively transmitdata through a speech codec in a communication network.

An efficient in-band modem is described in detail in U.S. patentapplication Ser. No. 12/477,544 which is assigned to the assignee hereofand hereby expressly incorporated by reference herein. The in-band modemallows information such as emergency information in an eCall applicationto be sent from a source to a destination and for the destination tosend a low layer acknowledgement at the in-band modem layer indicatingproper receipt of the transmitted information.

In some cases, it is advantageous for a layer higher than the low layer(modem layer), such as the application layer, to send an acknowledgementin addition to the low layer acknowledgement. Sending acknowledgementsfrom multiple layers allows for independence among the implementedlayers. For example, acknowledgement messaging at a Radio Link Protocol(RLP) layer may exist in addition to acknowledgement messaging at aTransmission Control Protocol (TCP) layer. Sending acknowledgements frommultiple layers also improves the reliability of the acknowledgmentmessaging by acting as a form of redundancy.

Multiple layer acknowledgement messaging increases the bandwidthrequirements of typical systems in the art. Typical systems transmitadditional identifier bits to distinguish a low layer message from ahigh layer message. For in-band modem systems, where the availablebandwidth is limited by the speech codec, incorporating multiple layeracknowledgement systems presents a costly overhead in the additionalbits required for the messages themselves as well as bits allocated todistinguish a low layer message from a high layer message. Compressionschemes on the acknowledgement messages have been proposed to reduce theoverhead. However, compression schemes do not distinguish differentmessage types at the modem layer and thus still result in an overallincrease in bandwidth requirements.

Accordingly it would be advantageous to provide an improved system forsupporting higher layer protocol messaging through a speech codec in acommunications network.

SUMMARY

Embodiments disclosed herein address the above stated needs by using anin-band modem to reliably transmit and receive higher layer protocolmessages through a speech codec.

In one embodiment, a method of acknowledging a source terminal datamessage from a destination terminal in an in-band communication systemcomprises transmitting a low layer acknowledgement (LLACK) signal,wherein the LLACK signal is comprised of a first synchronizationsequence followed by a LLACK message and transmitting a high layerapplication (HLMSG) signal, wherein the HLMSG signal is comprised of asecond synchronization sequence followed by a transformed HLMSG message.

In another embodiment, an apparatus comprises a transmitter configuredto transmit signals from a destination terminal, a receiver configuredto receive signals from a source terminal at the destination terminal, astart signal generator coupled to the transmitter and configured togenerate a start signal, a NACK signal generator coupled to thetransmitter and configured to generate a NACK signal, a data messagedetector coupled to the receiver and configured to detect a sourceterminal data message, a LLACK signal generator coupled to thetransmitter and configured to generate a first synchronization sequencefollowed by an LLACK message, and a HLACK signal generator coupled tothe transmitter and configured to generate a second synchronizationsequence followed by a transformed HLACK message.

In another embodiment, an apparatus comprises a processor, memory inelectronic communication with the processor, and instructions stored inthe memory, the instructions being capable of executing the steps oftransmitting a low layer acknowledgement (LLACK) signal, wherein theLLACK signal is comprised of a first synchronization sequence followedby a LLACK message and transmitting a high layer application (HLMSG)signal, wherein the HLMSG signal is comprised of a secondsynchronization sequence followed by a transformed HLMSG message,wherein the transformed HLMSG message is a high layer acknowledgement(HLACK) message.

In another embodiment, an apparatus for acknowledging a source terminaldata message from a destination terminal in an in-band communicationsystem comprises means for transmitting a low layer acknowledgement(LLACK) signal, wherein the LLACK signal is comprised of a firstsynchronization sequence followed by a LLACK message and means fortransmitting a high layer application (HLMSG) signal, wherein the HLMSGsignal is comprised of a second synchronization sequence followed by atransformed HLMSG message, wherein the transformed HLMSG message is ahigh layer acknowledgement (HLACK) message.

In another embodiment, a processor readable medium for acknowledging asource terminal data message from a destination terminal in an in-bandcommunication system, comprises instructions for transmitting a startsignal from the destination terminal, whereby the source terminal isconstrained to respond in a first predetermined manner, discontinuingtransmission of the start signal upon detection of a first receivedsignal, wherein the first received signal indicates a successfulreception of the start signal from the source terminal, transmitting anegative acknowledgement (NACK) signal from the destination terminal,whereby the source terminal is constrained to respond in a secondpredetermined manner, discontinuing transmission of the NACK signal uponsuccessful reception of the source terminal data message, transmitting alow layer acknowledgement (LLACK) signal, wherein the LLACK signal iscomprised of a first synchronization sequence followed by a LLACKmessage, transmitting a high layer application (HLMSG) signal, whereinthe HLMSG signal is comprised of a second synchronization sequencefollowed by a transformed HLMSG message, wherein the transformed HLMSGmessage is a high layer acknowledgement (HLACK) message, anddiscontinuing transmission of the LLACK signal upon detection of anuplink event

In another embodiment, a method of controlling source terminaltransmissions from a source terminal in an in-band communication systemcomprises detecting a request signal to transmit a user data message atthe source terminal, storing a message identifier at the sourceterminal, transmitting a synchronization signal from the source terminalupon detection of the request signal, transmitting the user data messagefrom the source terminal, and discontinuing transmission of the userdata message upon detection of a low layer acknowledgement (LLACK)signal or a high layer application (HLMSG) signal, wherein the LLACKsignal is comprised of a first synchronization sequence followed by aLLACK message, wherein the HLMSG signal is comprised of a secondsynchronization sequence followed by a transformed HLMSG message.

In another embodiment, an apparatus comprises a transmitter configuredto transmit signals from a source terminal, a receiver configured toreceive signals from a destination terminal at the source terminal, arequest signal detector configured to detect a request to transmit auser data message, a synchronization signal generator coupled to thetransmitter and configured to transmit a synchronization signal, a userdata message generator coupled to the transmitter and configured totransmit the user data message, a low layer acknowledgement (LLACK)signal detector coupled to the receiver and configured to detect a firstsynchronization sequence followed by an LLACK message, a high layeracknowledgement (HLACK) signal detector coupled to the receiver andconfigured to detect a second synchronization sequence followed by atransformed HLACK message.

In another embodiment, an apparatus comprises a processor, memory inelectronic communication with the processor, and instructions stored inthe memory, the instructions being capable of executing the steps ofdetecting a request signal to transmit a user data message at a sourceterminal, storing a message identifier at the source terminal,transmitting a synchronization signal from the source terminal upondetection of the request signal, transmitting the user data message fromthe source terminal, and discontinuing transmission of the user datamessage upon detection of a low layer acknowledgement (LLACK) signal ora high layer application (HLMSG) signal, wherein the LLACK signal iscomprised of a first synchronization sequence followed by a LLACKmessage, wherein the HLMSG signal is comprised of a secondsynchronization sequence followed by a transformed HLMSG message.

In another embodiment, an apparatus comprises means for detecting arequest signal to transmit a user data message at a source terminal,means for storing a message identifier at the source terminal, means fortransmitting a synchronization signal from the source terminal upondetection of the request signal, means for transmitting the user datamessage from the source terminal, means for detecting a low layeracknowledgement (LLACK) signal, wherein the LLACK signal is comprised ofa first synchronization sequence followed by a LLACK message, means fordetecting a high layer application (HLMSG) signal, wherein the HLMSGsignal is comprised of a second synchronization sequence followed by atransformed HLMSG message, wherein the transformed HLMSG message is ahigh layer acknowledgement (HLACK) message, and means for discontinuingtransmission of the user data message upon detection of the LLACK signalor HLMSG signal.

In another embodiment, a processor readable medium for controllingsource terminal transmissions from a source terminal in an in-bandcommunication system comprises instructions for detecting a requestsignal to transmit a user data message at the source terminal, storing amessage identifier at the source terminal, transmitting asynchronization signal from the source terminal upon detection of therequest signal, transmitting the user data message from the sourceterminal, discontinuing transmission of the user data message upondetection of a low layer acknowledgement (LLACK) signal or a high layerapplication (HLMSG) signal, wherein the LLACK signal is comprised of afirst synchronization sequence followed by a LLACK message, wherein theHLMSG signal is comprised of a second synchronization sequence followedby a transformed HLMSG message.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects and the attendant advantages of the embodiments describedherein will become more readily apparent by reference to the followingdetailed description when taken in conjunction with the accompanyingdrawings wherein:

FIG. 1A is a diagram of an embodiment of source and destinationterminals which use an in-band modem to transmit messages through aspeech codec in a wireless communication network.

FIG. 1B is a diagram of another embodiment of source and destinationterminals which use an in-band modem to transmit messages through aspeech codec in a wireless communication network.

FIG. 2 is a diagram of an embodiment of a transmit data modem used in anin-band communication system.

FIG. 3 is a diagram of an embodiment of a synchronization signalgenerator.

FIG. 4A is a diagram of an embodiment of a synchronization preamblesequence.

FIG. 4B is a diagram of an embodiment of a synchronization preamblesequence with non-overlapping reference sequences.

FIG. 5A is a graph of a synchronization preamble correlation outputwhere the preamble is comprised of non-overlapped reference sequences.

FIG. 5B is a graph of a synchronization preamble correlation outputwhere the preamble is comprised of overlapped reference sequences.

FIG. 6 is a diagram of an embodiment of a synchronization messageformat.

FIG. 7 is a diagram of an embodiment of a transmit data message format.

FIG. 8 is a diagram of an embodiment of a composite synchronization andtransmit data message format.

FIG. 9 is a diagram of an embodiment of a synchronization signaldetector and receiver controller.

FIG. 10 is a flowchart of an embodiment of a synchronization preambledetector.

FIG. 11 is a diagram of the Open System Interconnection (OSI) referencemodel.

FIG. 12A is a diagram of an embodiment of the communication and messagepassing between a Source and Destination Terminal where thecommunication link is initiated by the Source Terminal and the datatransfer link is initiated by the Destination Terminal.

FIG. 12B is a diagram of an embodiment of the communication and messagepassing between a Source and Destination Terminal where thecommunication link is initiated by the Destination Terminal and the datatransfer link is initiated by the Destination Terminal.

FIG. 12C is a diagram of an embodiment of the communication and messagepassing between a Source and Destination Terminal where thecommunication link is initiated by the Source Terminal and the datatransfer link is initiated by the Source Terminal.

FIG. 12D is a diagram of an embodiment of the communication and messagepassing between a Source and Destination Terminal where thecommunication link is initiated by the Destination Terminal and the datatransfer link is initiated by the Source Terminal.

FIG. 13 is a diagram of an embodiment of a transformation andregeneration of a high layer application message between a DestinationTerminal and a Source Terminal.

FIG. 14A is a diagram of an embodiment of an interaction of the datarequest sequence transmitted on a downlink in a destinationcommunication terminal and the data response sequence transmitted on anuplink in a source communication terminal, with the interactioninitiated by the destination terminal, wherein the downlink transmissionis comprised of a low layer acknowledgement message and a high layerapplication message, and the uplink transmission is terminated based onthe high layer application message.

FIG. 14B is a diagram of an embodiment of an interaction of the datarequest sequence transmitted on a downlink in a destinationcommunication terminal and the data response sequence transmitted on anuplink in a source communication terminal, with the interactioninitiated by the destination terminal, wherein the downlink transmissionis comprised of a low layer acknowledgement message and a high layeracknowledgement message, and the uplink transmission is terminated basedon the high layer acknowledgement message.

FIG. 14C is a diagram of an embodiment of an interaction of the datarequest sequence transmitted on a downlink in a destinationcommunication terminal and the data response sequence transmitted on anuplink in a source communication terminal, with the interactioninitiated by the destination terminal, wherein the downlink transmissionis comprised of a low layer acknowledgement message and a high layeracknowledgement message, and the uplink transmission is terminated basedon the low layer acknowledgement message.

FIG. 15 is a diagram of an embodiment of an interaction of the datarequest sequence transmitted on a downlink in a destinationcommunication terminal and the data response sequence transmitted on anuplink in a source communication terminal, with the interactioninitiated by the source terminal, wherein the downlink transmission iscomprised of a low layer acknowledgement message and a high layeracknowledgement message, and the uplink transmission is terminated basedon the high layer acknowledgement message.

FIG. 16A is a diagram of a second embodiment of a synchronizationpreamble sequence.

FIG. 16B is a graph of the correlation output for a second embodiment ofa synchronization preamble sequence.

FIG. 17A is a graph of a segment of a synchronization preamble sequence,wherein zero samples are placed between non-zero pulse samples.

FIG. 17B is a graph of a segment of a synchronization preamble sequence,wherein the zero samples placed between the non-zero pulse samples arereplaced with non-zero fixed amplitude samples.

FIG. 17C is a graph of a segment of a synchronization preamble sequence,wherein the zero samples placed between the non-zero pulse samples arereplaced with non-zero rectangular amplitude samples.

FIG. 17D is a graph of a segment of a synchronization preamble sequence,wherein the zero samples placed between the non-zero pulse samples arereplaced with non-zero random noise-like amplitude samples.

FIG. 17E is a graph of a segment of a synchronization preamble sequence,wherein the zero samples placed between the non-zero pulse samples arereplaced with non-zero sinusoidal amplitude samples.

FIG. 17F is a graph of a segment of a synchronization preamble sequence,wherein the non-zero pulse samples are increased in amplitude and thezero samples are replaced with non-zero fixed amplitude samples.

FIG. 18A is a flowchart of an embodiment of a first set of subtasks in amethod for a Destination Terminal signaling to a Source Terminal.

FIG. 18B is a flowchart of an embodiment of a second set of subtasks ina method for a Destination Terminal signaling to a Source Terminal.

FIG. 18C is a flowchart of an embodiment of a method M100 of aDestination Terminal signaling to a Source Terminal.

FIG. 18D is a flowchart of an embodiment of a method M200 of aDestination Terminal signaling to a Source Terminal.

FIG. 18E is a flowchart of an embodiment of a method M300 of aDestination Terminal signaling to a Source Terminal.

FIG. 19A is a block diagram of an embodiment of a first set of means ofan apparatus according to a first configuration.

FIG. 19B is a block diagram of an embodiment of a second set of means ofan apparatus according to a first configuration.

FIG. 19C is a block diagram of an embodiment of an apparatus A10.

FIG. 19D is a block diagram of an embodiment of an apparatus A20.

FIG. 19E is a block diagram of an embodiment of an apparatus A30.

FIG. 20A is a block diagram of an implementation of apparatus A10, A20,and A30 according to a first configuration.

FIG. 20B is a block diagram of an implementation of apparatus A10, A20,and A30 according to a second configuration.

FIG. 21A is a flowchart of an embodiment of a method M400 of a SourceTerminal signaling to a Destination Terminal.

FIG. 21B is a flowchart of an embodiment of a method M410 of a SourceTerminal signaling to a Destination Terminal.

FIG. 21C is a flowchart of an embodiment of a first set of subtasks formethod M410 of a Source Terminal signaling to a Destination Terminal.

FIG. 21D is a flowchart of an embodiment of a second set of subtasks formethod M410 of a Source Terminal signaling to a Destination Terminal.

FIG. 22A is a block diagram of an embodiment of an apparatus A40.

FIG. 22B is a block diagram of an embodiment of an apparatus A41.

FIG. 22C is a block diagram of an embodiment of a second set of means ofan apparatus A41.

FIG. 22D is a block diagram of an embodiment of a third set of means ofan apparatus A41.

FIG. 23A is a block diagram of an implementation of apparatus A40 andA41 according to a first configuration.

FIG. 23B is a block diagram of an implementation of apparatus A40 andA41 according to a second configuration.

FIG. 24A is a block diagram of an implementation of High layerapplication message regenerator according to a first configuration.

FIG. 24B is a block diagram of an implementation of High layerapplication message regenerator according to a second configuration.

FIG. 25 is a diagram of an embodiment of a telematics emergency callsystem.

DETAILED DESCRIPTION

Unless expressly limited by its context, the term “signal” is usedherein to indicate any of its ordinary meanings, including a state of amemory location (or set of memory locations) as expressed on a wire,bus, or other transmission medium. Unless expressly limited by itscontext, the term “generating” is used herein to indicate any of itsordinary meanings, such as computing or otherwise producing. Unlessexpressly limited by its context, the term “calculating” is used hereinto indicate any of its ordinary meanings, such as computing, evaluating,estimating, and/or selecting from a plurality of values. Unlessexpressly limited by its context, the term “obtaining” is used toindicate any of its ordinary meanings, such as calculating, deriving,receiving (e.g., from an external device), and/or retrieving (e.g., froman array of storage elements). Unless expressly limited by its context,the term “selecting” is used to indicate any of its ordinary meanings,such as identifying, indicating, applying, and/or using at least one,and fewer than all, of a set of two or more. Where the term “comprising”is used in the present description and claims, it does not exclude otherelements or operations. The term “based on” (as in “A is based on B”) isused to indicate any of its ordinary meanings, including the cases (i)“derived from” (e.g., “B is a precursor of A”), (ii) “based on at least”(e.g., “A is based on at least B”) and, if appropriate in the particularcontext, (iii) “equal to” (e.g., “A is equal to B”). Similarly, the term“in response to” is used to indicate any of its ordinary meanings,including “in response to at least.”

Unless indicated otherwise, any disclosure of an operation of anapparatus having a particular feature is also expressly intended todisclose a method having an analogous feature (and vice versa), and anydisclosure of an operation of an apparatus according to a particularconfiguration is also expressly intended to disclose a method accordingto an analogous configuration (and vice versa). The term “configuration”may be used in reference to a method, apparatus, and/or system asindicated by its particular context. The terms “method,” “process,”“procedure,” and “technique” are used generically and interchangeablyunless otherwise indicated by the particular context. The terms“apparatus” and “device” are also used generically and interchangeablyunless otherwise indicated by the particular context. The terms“element” and “module” are typically used to indicate a portion of agreater configuration. Unless expressly limited by its context, the term“system” is used herein to indicate any of its ordinary meanings,including “a group of elements that interact to serve a common purpose.”Any incorporation by reference of a portion of a document shall also beunderstood to incorporate definitions of terms or variables that arereferenced within the portion, where such definitions appear elsewherein the document, as well as any figures referenced in the incorporatedportion.

In a typical application a system, method, or apparatus is used tocontrol source terminal transmissions from a destination terminal in anin-band communication system. The system, method, or apparatus mayinclude acknowledgement signals sent by the Destination terminal whichmay be comprised of a low layer acknowledgement message, a high layeracknowledgement message which is transformed into a transformed highlayer acknowledgement message, or both low layer and high layeracknowledgement messages. The Destination terminal may distinguish thelow layer acknowledgement message from the transformed high layeracknowledgement message without sending additional identifierinformation bits by unique synchronization sequences pre-pended to theacknowledgement messages. The acknowledgement messages may bedistinguished by the Source terminal at the low layer by detecting theunique synchronization sequences. The Source terminal may reconstructthe high layer acknowledgement message from the transformed high layeracknowledgement message using a stored message identifier.

FIG. 1A shows an embodiment of an in-band data communication system asmight be implemented within a wireless source terminal 100. The sourceterminal 100 communicates with the destination terminal 600 through thecommunication channels 501 and 502, network 500, and communicationchannel 503. Examples of suitable wireless communication systems includecellular telephone systems operating in accordance with Global Systemfor Mobile Communication (GSM), Third Generation Partnership ProjectUniversal Mobile Telecommunication System (3GPP UMTS), Third GenerationPartnership Project 2 Code Division Multiple Access (3GPP2 CDMA), TimeDivision Synchronous Code Division Multiple Access (TD-SCDMA), andWorldwide Interoperability for Microwave Access (WiMAX) standards. Oneskilled in the art will recognize that the techniques described hereinmay be equally applied to an in-band data communication system that doesnot involve a wireless channel. The communication network 500 includesany combination of routing and/or switching equipment, communicationslinks and other infrastructure suitable for establishing a communicationlink between the source terminal 100 and destination terminal 600. Forexample, communication channel 503 may not be a wireless link. Thesource terminal 100 normally functions as a voice communication device.

Transmitter

The transmit baseband 200 normally routes user speech through a vocoder,but is also capable of routing non-speech data through the vocoder inresponse to a request originating from the source terminal or thecommunication network. Routing non-speech data through the vocoder isadvantageous since it eliminates the need for the source terminal torequest and transmit the data over a separate communications channel.The non-speech data is formatted into messages. The message data, stillin digital form, is converted into a noise-like signal comprised ofpulses. The message data information is built into the pulse positionsof the noise-like signal. The noise-like signal is encoded by thevocoder. The vocoder is not configured differently depending on whetherthe input is user speech or non-speech data so it is advantageous toconvert the message data into a signal which can be effectively encodedby the transmission parameter set allocated to the vocoder. The encodednoise-like signal is transmitted in-band over the communication link.Because the transmitted information is built in the pulse positions ofthe noise-like signal, reliable detection depends on recovery of thetiming of the pulses relative to the speech codec frame boundaries. Toaid the receiver in detecting the in-band transmission, a predeterminedsynchronization signal is encoded by the vocoder prior to thetransmission of message data. A protocol sequence of synchronization,control, and messages is transmitted to ensure reliable detection anddemodulation of the non-speech data at the receiver.

Referring to FIG. 1B, transmit baseband 200, the signal input audio 5210is input to the microphone and audio input processor 215 and transferredthrough the mux 220 into the vocoder encoder 270 where compressed voicedpackets are generated. A suitable audio input processor typicallyincludes circuitry to convert the input signal into a digital signal anda signal conditioner such as a low-pass filter. Examples of suitablevocoders include, but are not limited to, those described by thefollowing reference standards: GSM-FR, GSM-HR, GSM-EFR, EVRC, EVRC-B,SMV, QCELP13K, IS-54, AMR, G.723.1, G.728, G.729, G.729.1, G.729a,G.718, G.722.1, AMR-WB, EVRC-WB, VMR-WB. The vocoder encoder 270supplies voice packets to the transmitter 295 and antenna 296 and thevoice packets are transmitted over the communication channel 501.

A request for data transmission may be initiated by a user or sensorlocated near or within the source terminal or through the communicationsnetwork. The data transmit request S215 disables the voice path throughmux 220 and enables the transmit data path. The input data S200 ispre-processed by the data message formatter 210 and output as Tx MessageS220 to the Tx Data Modem 230. Input data S200 may include userinterface (UI) information, user position/location information, timestamps, equipment sensor information, or other suitable data. An exampleof a suitable data message formatter 210 includes circuitry to calculateand append cyclic redundancy check (CRC) bits to the input data, provideretransmission buffer memory, implement error control coding such ashybrid automatic repeat-request (HARQ), and interleave the input data.The Tx data modem 230 converts Tx Message S220 to data signal Tx DataS230 which is routed through mux 220 to the vocoder encoder 270. Oncethe data transmission is complete the voice path may be re-enabledthrough mux 220.

FIG. 2 is a suitable example block diagram of the Tx data modem 230shown in FIG. 1B. Three signals may be multiplexed in time through mux259 onto the Tx data S230 output signal; Sync Out S245, Mute Out S240,and Tx Mod Out S235. It should be recognized that different orders andcombinations of signals Sync Out S245, Mute Out S240, and Tx Mod OutS235 may be output onto Tx data S230. For example, Sync Out S245 may besent prior to each Tx Mod Out S235 data segment. Or, Sync Out S245 maybe sent once prior to a complete Tx Mod Out S235 with mute Out S240 sentbetween each Tx Mod Out S235 data segment.

Sync Out S245 is a synchronization signal used to establish timing atthe receiving terminal. Synchronization signals are required toestablish timing for the transmitted in-band data since the datainformation is built in the pulse positions of the noise-like signal.FIG. 3 shows a suitable example block diagram of the Sync Generator 240shown in FIG. 2. In a suitable example, FIG. 3 shows a Sync Generator240 comprised of Wakeup Out S236 and Sync Preamble Out S242 multiplexedin time where Wakeup Out S236 may be sent prior to each Sync PreambleOut S242.

Sync Preamble Out S242 may be used to establish fine (sample based)timing at the receiver and is comprised of a predetermined data patternknown at the receiver. A suitable example of a Sync Preamble Out S242predetermined data pattern is Sync Preamble Sequence 241 shown in FIG.4A. The composite preamble sequence 245 is generated by concatenatingseveral periods of a pseudorandom noise (PN) sequence 242 with anoverlapped and added result of the PN sequence 242 and an invertedversion of the PN sequence 244. The ‘+’ symbols in the compositepreamble sequence 245 may represent binary data +1 and the ‘−’ symbolsrepresent binary data −1. In a suitable example, the overlap and add ofa ‘+’ symbol with another ‘+’ symbol yields a ‘+’ symbol, and similarlythe overlap and add of a ‘−’ symbol with another ‘−’ symbol yields a ‘−’symbol. Another suitable example inserts zero valued samples between thedata bits of the PN sequence. This provides temporal distance betweenthe data bits to account for “smearing” affects caused by the bandpassfilter characteristics of the channel which tends to spread the energyof the data bit over several bit time intervals.

The previously described construction of the sync preamble usingconcatenated periods of a PN sequence with overlapped segments ofinverted versions of the PN sequence provides advantages in reducedtransmission time, improved correlation properties, and improveddetection characteristics. The advantages result in a preamble which isrobust to speech frame transmission errors.

By overlapping the PN segments, the resultant composite sync preambleconsists of a smaller number of bits in the sequence compared to anon-overlapped version, thereby decreasing the total time required totransmit the composite preamble sequence 245.

To illustrate the improvements in the correlation properties of theoverlapped sync preamble, FIG. 5A and FIG. 5B show a comparison betweenthe correlation of PN sequence 242 with a non-overlapped compositepreamble sequence 245 b, shown in FIG. 4B and the correlation of PNsequence 242 with the overlapped composite sync preamble sequence 245,shown in FIG. 4A. FIG. 5A shows the main correlation peaks, bothpositive and negative, as well as the minor correlation peaks locatedbetween the main peaks for the non-overlapped composite sync preamblesequence 245 b. The negative peak 1010 results from the correlation ofthe PN sequence 242 with the first inverted segment of thenon-overlapped composite preamble sequence 245 b. The positivecorrelation peaks 1011, 1012, 1013, result from the correlation of thePN sequence 242 with the three concatenated segments of PN sequence 242which make up the middle section of the non-overlapped compositepreamble sequence 245 b. The negative peak 1014 results from thecorrelation of the PN sequence 242 with the second inverted segment ofthe non-overlapped composite preamble sequence 245 b. In FIG. 5A, theminor correlation peak 1015, corresponding to an offset of 3 samplesfrom the first positive correlation peak 1011, shows a magnitude ofapproximately 5 (⅓rd the magnitude of the main peaks). FIG. 5B showsseveral main correlation peaks, both positive and negative, as well asthe minor correlation peaks between the main peaks for the overlappedcomposite sync preamble sequence 245. In FIG. 5B, the minor correlationpeak 1016, corresponding to an offset of 3 samples from the firstpositive correlation peak 1011, shows a magnitude of approximately 3(⅕th the magnitude of the main peaks). The smaller magnitude of theminor correlation peak 1016 for the overlapped preamble shown in FIG. 5Bresults in less false detections of the preamble main correlation peakswhen compared to the non-overlapped minor peak 1015 example shown inFIG. 5A.

As shown in FIG. 5B, five major peaks are generated when correlating PNsequence 242 with the composite sync preamble sequence 245. The patternshown (1 negative peak, 3 positive peaks, and 1 negative peak) allowsfor determining the frame timing based on any 3 detected peaks and thecorresponding temporal distances between the peaks. The combination of 3detected peaks with the corresponding temporal distance is alwaysunique. A similar depiction of the correlation peak pattern is shown inTable 1, where the correlation peaks are referenced by a ‘−’ for anegative peak and a ‘+’ for a positive peak. The technique of using aunique correlation peak pattern is advantageous for in-band systemssince the unique pattern compensates for possible speech frame losses,for example, due to poor channel conditions. Losing a speech frame mayresult in losing a correlation peak as well. By having a unique patternof correlation peaks separated by predetermined temporal distances, areceiver can reliably detect the sync preamble even with lost speechframes which result in lost correlation peaks. Several examples areshown in Table 2 for the combinations of 3 detected peaks in the pattern(2 peaks are lost in each example). Each entry in Table 2, represents aunique pattern of peaks and temporal distances between the peaks.Example 1 in Table 2 shows detected peaks 3, 4, and 5 (peaks 1 and 2were lost), resulting in the pattern ‘+ + −’ with one predetermineddistance between each peak. Examples 2 and 3 in Table 2 also show thepattern ‘+ + −’, however the distances are different. Example 2 has twopredetermined distances between detected peak 2 and 4, while Example 3has two predetermined distances between detected peak 3 and 5. SoExamples 1, 2 and 3 each represent a unique pattern from which the frametiming may be derived. It should be recognized that the detected peaksmay extend across frame boundaries, but that the unique patterns andpredetermined distances still apply.

TABLE 1 Correlation Peak Number 1 2 3 4 5 Correlation Peak Polarity− + + + −

TABLE 2 Correlation Peak Number 1 2 3 4 5 Detected Example 1 + + −Correlation Example 2 + + − Peaks Example 3 + + − Example 4 + + +Example 5 − + − Example 6 − + − Example 7 − + + Example 8 − + − Example9 − + + Example 10 − + +

One skilled in the art will recognize that a different preamble sequenceresulting in a different correlation peak pattern to that shown in FIG.5B and Table 1 may be used. One skilled in the art will also recognizethat multiple correlation peak patterns may be used to identifydifferent operational modes or transmit information bits. An example ofan alternate correlation peak pattern is shown in Table 3. Thecorrelation peak pattern shown in Table 3 maintains a unique patternfrom which the frame timing may be derived, as described previously.Having multiple correlation peak patterns is advantageous foridentifying different transmitter configurations at the receiver, suchas message formats, message types, or modulation schemes.

TABLE 3 Correlation Peak Number 1 2 3 4 5 Correlation Peak Polarity + −− − +

Referring again to FIG. 3, Wakeup Out S236 may be used to trigger thevocoder encoder 270 to wake up from a sleep state, low transmission ratestate, or discontinuous transmission state. Wakeup Out S236 may also beused to prohibit the vocoder encoder 270 from entering the sleep, lowtransmission, or discontinuous transmission state. Wakeup Out S236 isgenerated by Wakeup Generator 256. Wakeup signals are advantageous whentransmitting in-band data through vocoders which implement sleep,discontinuous transmit functions (DTX), or operate at a lowertransmission rate during inactive voice segments to minimize the startupdelay which may occur in transitioning from the voice inactive state tothe voice active state. Wakeup signals may also be used to identify acharacteristic of the transmission mode; for example, the type ofmodulation scheme employed. A first example of a suitable Wakeup OutS236 signal is a single sinusoidal signal of constant frequency in thevoice band, such as 395 Hz. In this first example, the Wakeup signalprohibits the vocoder encoder 270 from entering the sleep, DTX, or lowrate state. In this first example, the receiver ignores the transmittedWakeup Out signal 5236. A second example of a suitable Wakeup Out S236is a signal comprised of multiple sinusoidal signals with each signalidentifying a specific data modulation scheme, for example 500 Hz formodulation scheme 1 and 800 Hz for modulation scheme 2. In this secondexample, the Wakeup signal prohibits the vocoder encoder 270 fromentering the sleep, DTX, or low rate state. In this second example, thereceiver uses the transmitted Wakeup Out signal S236 to identify thedata modulation scheme.

An example of a composite Sync Out S245 signal is one comprised of amultiplexed Wakeup Out S236 and Sync Preamble Out S242 as shown in FIG.6. Twu 711 and Tsp 702 represent the durations in time each signal istransmitted. An example of a suitable range for Twu is 10-60milliseconds and Tsp is 40-200 milliseconds.

Referring back to FIG. 2, a suitable example of Tx Mod Out S235 is asignal generated by the Modulator 235 using pulse-position modulation(PPM) with special modulation pulses. This modulation technique resultsin low distortion when encoded and decoded by different types ofvocoders. Additionally, this technique results in good autocorrelationproperties and can be easily detected by a receiver matched to thewaveform. Further, the pulses do not have a tonal structure; instead thesignals appear noise-like in the frequency spectrum domain as well asretain a noise-like audible characteristic.

Referring again to FIG. 2, Mute Out S240 is a signal which may be usedto separate the Tx message transmissions and is generated by the MutingGenerator 255. An example of a suitable composite Tx Data S230 signalcomprised of a multiplexed Tx Mod Out S235 and Mute Out S240 is shown inFIG. 7. Tmu1 731, Td1 732, Tmu2 733, Td2 734, Tmu3 735, Td3 736, andTmu4 737 represent the durations in time each signal is transmitted. Anexample of a suitable range for Tmu1, Tmu2, Tmu3, and Tmu4 is 10-60milliseconds and Td1, Td2, and Td3 is 300-320 milliseconds for normaloperation and 600-640 milliseconds for robust operation. Examples of asuitable muting generator sequence may be an all-zero sequence signal ora sinusoidal frequency signal. Another suitable example of a signal usedto separate the Tx message transmissions is shown in FIG. 8. In thisexample, the Wakeup Out S236 signal and Sync Preamble Out S242 precedeeach transmission of Tx Mod Out S235. One skilled in the art willrecognize that different combinations of the Sync Preamble Out S242,Mute Out S240, and Tx Mod Out S235 may be equally applied. For exampleTx Mod Out S235 in FIG. 8 may be preceded and followed by Mute Out S240.

Receiver

Referring to FIG. 1A, the receive baseband 400 normally routes decodedvoice packets from the vocoder to an audio processor, but is alsocapable of routing the decoded packets through a data demodulator. Ifthe non-speech data was converted to a noise-like signal and encoded bythe vocoder at the transmitter as described herein, the receiver'svocoder is able to effectively decode the data with minimal distortion.The decoded packets are continually monitored for an in-bandsynchronization signal. If a synchronization signal is found, the frametiming is recovered and the decoded packet data is routed to a datademodulator. The decoded packet data is demodulated into messages. Themessages are deformatted and output. A protocol sequence comprisingsynchronization, control, and messages ensures reliable detection anddemodulation of the non-speech data.

Referring to FIG. 1B, voice packets are received over the communicationchannel 502 in the receiver 495 and input to the vocoder decoder 390where decoded voice is generated then routed through the de-mux 320 tothe audio out processor and speaker 315 generating output audio 5310.

Once a synchronization signal is detected in Vocoder Decoder Output S370by the Sync Detector 350, the Rx De-Mux Control S360 signal switches tothe Rx data path in the Rx De-Mux 320. The vocoder packets are decodedby the vocoder decoder 390 and routed by the Rx De-Mux 320 to the RxTiming 380 then the Rx data modem 330. The Rx data is demodulated by theRx data modem 330 and forwarded to the data message deformatter 301where output data S300 is made available to the user or interfacedequipment.

An example of a suitable data message deformatter 301 includes circuitryto deinterleave the Rx Message S320 data, implement error controldecoding such as hybrid automatic repeat-request (HARQ), and calculateand check the cyclic redundancy check (CRC) bits. Suitable output dataS300 may include user interface (UI) information, user position/locationinformation, time stamps, equipment sensor information, or othersuitable data.

An example of a suitable Sync Detector 350 is shown in FIG. 9. SignalVocoder Decoder Output S370 is input to a Memory 352 and a Sync PreambleDetector 351. The Memory 352 is used to store the latest Vocoder DecoderOutput S370 samples which may include the received Wakeup Out signal. Asuitable example of the Memory 352 is a First-In-First-Out (FIFO) orRandom Access Memory (RAM). The Sync Preamble Detector 351 detects thetransmitted Sync Preamble Out signal in the Vocoder Decoder Output S370and outputs the SyncFlag S305 signal. Signals Modulation Type S306 andSyncFlag S305 are input to the Sync Detector Controller 370. The SyncDetector Controller 370 generates the Modulation Search S307 signalwhich may be used to access the Memory 352, find the received Wakeup Outsignal based on the Timing Offset S350, and evaluate the Wakeup OutSignal to determine the type of modulation used in the transmission. Theresulting detected modulation type may be output from the Memory 352 asModulation Type S306. The Sync Detector Controller 370 also generatesoutput signals Rx De-Mux Control S360 which controls routing of theVocoder Decoder Output S370 to the data path or the audio path, AudioMute Control S365 which enables or disables the output audio signalS310, and Timing Offset S350 which provides bit timing information to RxTiming 380 to align the Rx Data S326 for demodulation.

An example of a suitable Sync Preamble Detector 351 is shown in FIG. 10.Signal Vocoder Decoder Output S370 is processed by the filter in step452. A suitable example of the filter in step 452 is a sparse filterwith coefficients based on the band-pass filtered impulse response ofthe Sync Preamble Sequence. A sparse filter has afinite-impulse-response structure with some of the coefficients set tozero and results in a reduction in the computational complexity based onfewer required multipliers due to the zero coefficients. Sparse filtersare well known in the art. In step 453 the filter output is searched forthe maximum positive and negative correlation peaks which match anexpected pattern based on the negative and positive correlation peakdistance. For example, 5 peaks should be found in step 453 based on SyncPreamble Sequence 245, 3 positive peaks corresponding to correlationwith the pseudorandom noise (PN) sequence 243 and 2 negative peakscorresponding to correlation with the inverted version of the PNsequence 244. In step 461, the number of peaks detected is counted andif a majority of peaks is detected, then a sync indicator flag is setTrue in step 460, indicating the preamble sync has been detected. Asuitable example of a majority of peaks detected is 4 out of 5 peakswhich match the expected pattern. If a majority of peaks is not detectedthen control passes to step 454, where the temporal distance between thepositive peaks found in step 453 is compared against the expecteddistance, PeakDistT1. The PeakDistT1 is set to be a function of theperiod of the PN sequence 242 since filtering the received preambleagainst PN sequence 242 should yield a temporal distance between thecorrelation peaks which is equal to some multiple of the period. If thetemporal distance between the positive peaks is found to be within arange of PeakDistT1, the positive peaks amplitudes are then checkedagainst a threshold PeakAmpT1 in step 455. A suitable range forPeakDistT1 is plus or minus 2 samples. The PeakAmpT1 is a function ofthe amplitudes of the previous peaks found. In a suitable example, thePeakAmpT1 is set such that the peaks found in step 453 do not differ inamplitude by more than a factor of 3 and the average peak amplitude doesnot exceed half the maximum peak amplitude observed up to that point. Ifeither the positive peak temporal distance check in step 454 or theamplitude check in step 455 fails then the negative peak temporaldistance is checked in step 456. If the negative peak temporal distanceis within a range of PeakDistT2 then the negative peak amplitudes arechecked against a threshold PeakAmpT2 in step 457. A suitable range forPeakDistT2 is plus or minus 2 samples. PeakDistT2 is set to be afunction of the period of the PN sequence 242 and the PeakAmpT2 is setto be a function of the amplitudes of the previous peaks found. Ifeither the positive peak temporal distance check in step 454 and thepositive peak amplitude check in step 455 or the negative peak temporaldistance check in step 456 and the negative peak amplitude check in step457 pass then a sync indicator flag is set True in step 460, indicatingthe preamble sync has been detected. If either the negative peaktemporal distance check in step 456 or negative peak amplitude check instep 457 fails then the sync indicator flag is set False in step 458,indicating the preamble sync has not been detected. It should berecognized that different orders and combinations of the steps willachieve the same result. For example, detecting the majority of peaks instep 461 may be done after the positive peak check of steps 454 and 455.

System

The communication between the Source Terminal 100 and DestinationTerminal 600 may be accomplished by implementing a protocol stack withineach terminal. Protocol stacks serve to partition functional elements orto separate higher layers (such as a software application) from lowerlayers (such as a modem).

FIG. 11 shows a block diagram of the well known Open SystemInterconnection (OSI) reference model. The model shows the protocolstack; that is, the interconnection between the various layers for anindividual Sender and Receiver as well as the physical connection and anexample virtual connection between the Sender and Receiver. In the OSImodel, an individual layer can support communication only to layersimmediately above and below it. The actual (physical) connection betweenthe Sender and Receiver is provided by the Physical Layer, while anotherhigher layer may maintain a virtual connection by flowing messagesthrough the lower layers. For example, a Sender Transport Layer messageis sent to the Receiver Transport layer via the Sender Network, DataLink, and Physical Layers, across to the Receiver Physical Layer then upthe Receiver Data Link, Network and Transport layers.

FIG. 12A is an example interaction diagram of the communication andmessage passing between the Source Terminal 100 and the DestinationTerminal 600, wherein the Source Terminal 100 and the DestinationTerminal 600 protocol stack is comprised of a high layer and a lowlayer. In this example, the communication link is initiated by theSource Terminal 100 and the data transfer link is initiated by theDestination Terminal 600. A suitable example of a communication link isone which is defined by one of the standards organizations listed hereinwhich incorporates a voice service option; that is, a vocoder. Anelement, for example a software application, in the Source Terminal 100high layer sends a Call Setup 1100 message to an element, for example amodem, in the low layer. The Source Terminal 100 low layer initiatesestablishment of the communication link to the Destination Terminal 600by sending an Initiate 1105 message. The Initiate 1105 message isreceived by the Destination Terminal 600 and the communication link isestablished per the recommendations described in the communicationstandard specifications listed herein. The high layer in the SourceTerminal 100 sends the data to be transmitted to the low layer. Asuitable example of data may include a minimum set of data or “MSD”message as described in an emergency telematics system such as eCall.The Source Terminal 100 low layer stores an identifier associated withthe MSD in a local storage medium 1115. In a suitable example system, asingle acknowledgement is sent by the Destination Terminal 600 low layerfor each MSD message received; that is, a new MSD will not be sent bythe Source Terminal 100 until it receives at least a low layeracknowledgement message for the current MSD. If an MSD identifier isstored by Source Terminal 100 in a local storage medium 1115, then theDestination Terminal 600 would not be required to return the MSDidentifier in the low layer acknowledgement message since the identifierwould already be accessible to the Source Terminal 100 low layer fromthe local storage medium 1115. Eliminating the need to transmit the MSDidentifier in an acknowledgement message results in an advantageousbandwidth savings. The transfer of the MSD message is initiated by theDestination Terminal 600 low layer with the transmission of a Start 802message to the Source Terminal 100. The Source Terminal 100 low layerresponds to the received Start 802 message by sending the MSD messagedata 812. The Destination Terminal 600 low layer responds to thereceived MSD data 812 by verifying correct reception of the MSD,forwarding the MSD to the high layer, and sending a low layeracknowledgement (LLACK) signal comprised of a first synchronizationsequence and an LLACK message. The Destination Terminal 600 low layersends the LLACK 804 to the Source Terminal 100 in order to establish afirst level of acknowledgement between the Source Terminal 100 and theDestination Terminal 600 low layers. The Destination Terminal 600 highlayer may send a high layer application message 1220 to the low layer inresponse to the received MSD where it is transformed in the low layer bya Transform HLMSG 1230 element. The resultant Transformed HLMSG 894 issent to the Source Terminal 100 preceded by a second synchronizationsequence which is different from the first synchronization sequence sentwith the LLACK . The Source Terminal 100 receives and identifies theTransformed HLMSG 894 by detecting the second synchronization sequenceassigned to the Transformed HLMSG 894. The low layer retrieves the MSDidentifier 1120 from the local storage medium 1115 then regenerates theHLMSG from the stored MSD identifier 1120 and the received TransformedHLMSG 894 and forwards the regenerated HLMSG 1125 to the high layer. Theregenerated HLMSG 1125 establishes a second level of communicationbetween the Source Terminal 100 and the Destination Terminal 600 highlayers. In this example, the Destination Terminal 600 HLMSG 1220 messageand the Source Terminal 100 regenerated HLMSG 1125 message areequivalent. In a suitable example, the HLMSG is comprised of a highlayer acknowledgement message (HLACK). One skilled in the art willrecognize that the interactions between the Source Terminal 100 and theDestination Terminal 600 may occur in a different order. For example,the Start 802 message may occur prior to the storage of the MSDidentifier.

The Transform HLMSG 1230 element may modify the parameters in the highlayer HLMSG 1220 message, reduce the number of parameters sent, orcompress the parameters themselves. FIG. 13 is a diagram of an exampletransformation and regeneration of the HLMSG message between theDestination Terminal 600 and the Source Terminal 100. In this example,the Destination Terminal 600 HLMSG 1220 message is comprised of a formatfield, a message ID, a status field, and a CRC calculated over theformat, message ID and status fields. The Transform HLMSG 1230 elementmay reduce the format field from 1 byte to 1 bit and the status fieldfrom 1 byte to 3 bits. The resultant Transformed HLMSG 894 is sent tothe Source Terminal 100. The Source Terminal 100 regenerates the HLMSG1125 message from the received Transformed HLMSG 894 format and statusbits and the locally stored MSD 1120. The CRC in the regenerated HLACK1125 message may be recalculated at the Source Terminal 100 low layerfrom the regenerated format, message ID, and status fields. One skilledin the art will recognize that the format and/or status fields may notbe reduced as is described in the example herein, or that only a statusfield may be sent if, for example, the message formats are fixed betweenthe Source Terminal 100 and Destination Terminal 600 low layersresulting in no need to specifically identify the message formats with aformat field.

FIG. 12B is an example interaction diagram of the communication andmessage passing between the Source Terminal 100 and the DestinationTerminal 600, wherein the communication link is initiated by theDestination Terminal 600 and the data transfer link is initiated by theDestination Terminal 600. The interactions are similar to thosedescribed for FIG. 12A except that an element in the DestinationTerminal 600 high layer sends a Call Setup 1100 message to an element inthe low layer. The Destination Terminal 600 low layer initiatesestablishment of the communication link to the Source Terminal 100 bysending an Initiate 1105 message.

FIG. 12C is an example interaction diagram of the communication andmessage passing between the Source Terminal 100 and the DestinationTerminal 600, wherein the communication link is initiated by the SourceTerminal 100 and the data transfer link is initiated by the SourceTerminal 100. The interactions are similar to those described for FIG.12A except that the Source Terminal 100 initiates the data transferlink. The Source Terminal 100 high layer sends the MSD message to thelow layer and an MSD identifier is stored in a local storage medium1115. The Source Terminal 100 low layer initiates the MSD transfer bysending a SEND 805 message to the Destination Terminal 600. TheDestination Terminal 600 responds to the SEND 805 message by sending theStart 802 message and the subsequent interactions occur as described forFIG. 12A.

FIG. 12D is an example interaction diagram of the communication andmessage passing between the Source Terminal 100 and the DestinationTerminal 600, wherein the communication link is initiated by theDestination Terminal 600 and the data transfer link is initiated by theSource Terminal 100. The interactions are similar to those described forFIG. 12A except that the communication link is initiated as describedfor FIG. 12B and the data transfer link is initiated as described forFIG. 12C.

In receiving the LLACK and HLMSG messages, the Source Terminal 100 mustbe able to distinguish the two messages so that the HLMSG can beforwarded to the high layer. A typical system may transmit additionalidentifier bits to distinguish the two messages. In an in-band modemwhere the available bandwidth is limited, a mechanism to identify thetwo messages without increasing the bandwidth requirements is desirableand advantageous. Unique synchronization signals may be assigned to eachof the messages which allows the sync detector to discriminate betweenthe LLACK and the HLMSG message. For the low layer acknowledgement(LLACK) message, a first synchronization signal may be sent. FIG. 4Ashows a suitable example of a first synchronization signal 245. For thehigh layer message (HLMSG), a second synchronization signal may be sent.A suitable example of a second synchronization signal is shown in FIG.16A. The sync detector described herein discriminates the polarity ofthe correlation peak pattern shown in FIG. 5A resulting from the firstsynchronization signal 245 from the polarity of the correlation peakpattern shown in FIG. 16B resulting from the second synchronizationsignal shown in FIG. 16A. The Source Terminal 100, is thus able todistinguish the LLACK message from the HLMSG message without the needfor the Destination Terminal 600 to transmit additional acknowledgementidentifier bits. Eliminating the need to transmit additional bits toidentify lower layer from higher layer messages results in anadvantageous bandwidth savings.

In some cases a data sample inversion may occur in the network resultingin inverted polarity in the received synchronization preamble and datamessages. In the previous case described, sample data (e.g. the secondsynchronization signal) may be purposely inverted in order to expand themessage space without expending extra bits to identify additionalmessages. In the purposely inverted case, a new set of messages isdefined with the “negative polarity” synchronization such that areceiver could identify the polarity and thus determine whether themessage data refers to a low layer message or a high layer message. Thecorrelation peaks are detected as previously described. If networkinduced inversion of the data occurs, then a detection logic mechanismto determine whether the inversion was intentional is desirable. Thedetector 351 shown in FIG. 10 may be carried out twice, once assumingthe positive correlation peak pattern show in FIG. 5B and another timeassuming the negative correlation peak pattern shown in FIG. 16B. Thefirst run of the decision logic returns the original sync detectionresult whereas the second run returns the detection result assuming thesignal was inverted. The decision logic then determines whether thefirst or second detection result is valid. If the second detectionresult is chosen, the received data samples are inverted before they areinput to the demodulator. In some cases, both runs of thesynchronization detection logic may return successful synchronizationevents, for example, due to the band pass characteristics of the speechchannel. Therefore, additional decision logic may be used to make thefinal detection decision. This additional decision is amplitude basedand also takes into account how many peaks have been detected. In thedownlink (e.g. from Destination terminal 600 to Source terminal 100),treatment of the data messages following the sync may be dependent onthe detected polarity. If the sync is detected with positive polaritythen the receiver prepares to receive a low layer message. If the syncis detected with negative polarity then the receiver prepares to receiveeither a high layer message if the sync is not the first received or thereceiver prepares to invert the subsequent data if the sync is the firstreceived, indicating a polarity inversion in the system. In the uplink(e.g. from Source terminal 100 to Destination terminal 600), thedetection of a negative polarity sync may be an indication of aninverted data stream (i.e. it may not indicate a high layer message)only, or may be an indication of an inverted data stream or high layermessage.

Assigning unique synchronization sequences as described previously maynot only be applied to a single terminal (e.g. for the first and secondsynchronization sequences of a Destination transmission), but also mayenable a more robust transmission of data between a Source andDestination terminal through different cellular networks (e.g. a Sourceterminal may use a first synchronization sequence and a Destinationterminal may use a synchronization sequence which is different from thesequence used at the Source terminal). Most cellular networksincorporate echo cancellers in the voice signal path which attempt toremove unwanted signals typically comprised of reflected versions of atransmitted signal. An uplink signal may be reflected on the downlinkdue to an impedance mismatch at the physical connection between a mobiletelephone switching office and a backhaul, wherein the connection maycomprise a two-wire to four-wire interface conversion known in the artas a hybrid. Backhauls are well known in the art and compriseintermediate communication links between the core network and smallersubnetworks at or towards the edge of a system. For an in-bandcommunication system, the uplink signal may be reflected back on thedownlink due to the hybrid. An echo canceller located at the cellularbase station attempts to correlate a Far-end signal (e.g. the uplinktransmission) with a Near-end signal (e.g. the downlink transmission oralternatively the reflected uplink signal) to determine if an echoexists and subtracts the estimated echo using adaptive filtertechniques, such as the well known Least Means Square (LMS) algorithm.The echo canceller may also use non-linear processing elements such asfrequency domain spectral subtraction to further reduce the echo. Anin-band system may use a synchronization signal that is similar (e.g.correlated) for both the uplink and downlink. In this case, the systemmay experience cropping (losing the beginning and/or end of atransmission), dropouts (losing a middle section of a transmission), ordistortions in the signal due to the adaptive filter and non-linearprocessing in the echo canceller. In other words, if a received Far-endsignal is similar (e.g. correlated) to the received Near-end signal, theecho canceller may determine that the Near-end signal is a reflectedversion of the Far-end signal and attempt to cancel it resulting incropping, dropouts, or distortions in the Near-end signal. Further, mosttypical echo cancellers disable part of the processing during a statewhen both uplink and downlink contain appreciable signal (e.g. speech)activity, known in the art as doubletalk. A doubletalk conditiontypically results in a controller in the echo canceller freezing theprocessing of the non-linear element and/or the coefficients of theadaptive filter which may result in less signal cropping, dropouts, ordistortions of the Near-end signal. Accordingly, it is advantageous toconstruct synchronization sequences for an uplink and downlink in anin-band system which are dissimilar to minimize correlation propertiesbetween the sequences and/or provoke a doubletalk condition in an echocanceller so that cropping, dropouts, or distortions in the downlinksignal does not occur, yet still exhibits a structure which isdetectable by the sync detector disclosed herein.

Suitable examples of alternative synchronization sequences are shown inFIG. 17A, FIG. 17B, FIG. 17C, FIG. 17D, FIG. 17E, and FIG. 17F. Asegment of the synchronization signal described in FIG. 4A is shown inFIG. 17A. In order to distinguish the synchronization sequences betweenthe uplink and downlink, one of the synchronization sequences may beconstructed such that the zero valued samples placed between thenon-zero pulses are replaced by samples with non-zero values. Thestructure of the original synchronization sequence (i.e. the non-zeropulse sequence) is, however, left intact so that the sync detectordescribed herein is still able to detect the signal. The replacing ofzero samples with non-zero samples results in effectively adding moreenergy to the signal, and thereby reduces the correlation between theuplink and downlink synchronization signals such that an echo cancellerwill not erroneously identify the downlink signal as a reflected uplinksignal. FIG. 17B shows a suitable example of a modified synchronizationsignal, wherein the zero valued samples are replaced by samples of fixedamplitude 12000. The actual fixed value of the amplitude may comprise avalue different from 12000, but should not be too large in order for theoriginal synchronization signal to remain observable, thus allowing thesync detector described herein to detect the sync signal. FIG. 17C showsanother suitable example of a modified synchronization signal, whereinthe zero valued samples are replaced by a rectangular signal. Again,different amplitudes may be chosen. FIG. 17D shows yet another suitableexample of a modified synchronization signal, wherein the zero valuedsamples are replaced by a random noise-like signal. FIG. 17E shows yetanother suitable example of a modified synchronization signal, whereinthe zero valued samples are replaced by a sinusoidal signal. Finally,FIG. 17F shows yet another suitable example of a modifiedsynchronization signal, wherein the pulses are also increased inamplitude.

FIG. 14A is an example interaction diagram of the synchronization anddata transmission sequences between the Source Terminal 100 and theDestination Terminal 600. The Downlink Transmission sequence 800represents the transmission of sync and data messages from theDestination Terminal 600 to the Source Terminal 100 and the UplinkTransmission sequence 810 represents the transmission of sync and datamessages from the Source Terminal 100 to the Destination Terminal 600.In this example, the Uplink Transmission sequence 810 is initiated bythe Destination Terminal 600. The Downlink Transmission sequence 800 isinitiated at time t0 850 by the Destination Terminal 600 with a firstsync sequence 801. A suitable example of the first sync sequence 801 isdescribed in FIG. 6 with Sync Preamble Out as shown in FIG. 4A. Anothersuitable example of the first sync sequence 801 is described in FIG. 6with Sync Preamble Out as shown in FIG. 17A, FIG. 17B, FIG. 17C, FIG.17D, FIG. 17E, or FIG. 17F. Following the first sync sequence 801, theDestination Terminal 600 transmits a “Start” message 802 to command theSource Terminal 100 to begin transmitting its Uplink Transmission 810sequence. The Destination Terminal 600 continues to transmit analternating first sync 801 and “Start” message 802 and waits for aresponse from the Source Terminal 100. At time t1 851 the SourceTerminal 100, having received the “Start” message 802 from theDestination Terminal 600, begins transmitting its own sync sequence 811.A suitable example of the sync sequence 811 is described in FIG. 6 withSync Preamble Out as shown in FIG. 4A, but may also comprise a SyncPreamble Out which is different from that which is transmitted on thedownlink. Following the sync sequence 811, the Source Terminal 100transmits a minimum set of data or “MSD” message 812 to the DestinationTerminal 600. A suitable example of data comprising the MSD message 812includes user data formatted by a data message formatter 210. At time t2852 the Destination Terminal 600, having received the sync message 811from the Source Terminal 100, begins transmitting a negativeacknowledgement or “NACK” message 803 to the Source Terminal 100. TheDestination Terminal 600 continues to transmit an alternating first sync801 and “NACK” message 803 until it successfully receives the MSDmessage 812 from the Source Terminal 100. A suitable example ofsuccessfully receiving the MSD message 812 includes verifying a cyclicredundancy check performed on the MSD message 812. At time t3 853, theDestination Terminal 600, having successfully received the MSD message,begins transmitting a low layer acknowledgement or “LLACK signal”comprised of a first sync 801 and low layer acknowledgement “LLACK”message 804. At time t5 855, the Destination Terminal 600 beginstransmitting a high layer message or “HLMSG signal” comprised of asecond sync 893 and high layer message HLMSG 894. A suitable example ofa second sync signal 893 is an inverted sequence to that shown in 245(‘+’ and ‘−’ polarity bits swapped) as shown in FIG. 16A which resultsin the alternate correlation peak pattern shown in FIG. 16B and Table 3.Another suitable example of a second sync signal 893 is an invertedsequence to that shown in 245 (‘+’ and ‘−’ polarity bits swapped) withzero samples replaced by non-zero samples as shown in FIG. 17A, FIG.17B, FIG. 17C, FIG. 17D, FIG. 17E, or FIG. 17F. The Source Terminal 100may attempt to send the MSD message 812 multiple times (813, 814) untilit receives the LLACK message. In alternate embodiments, the SourceTerminal 100 may attempt to send the MSD message 812 multiple times(813, 814) until it receives an HLMSG message, or both LLACK and HLMSGmessages. In a suitable example, if the Source Terminal 100 attempts tosend the MSD message more than eight times wherein each attempt is adifferent redundancy version, it switches to a more robust modulationscheme identified by the Wakeup signal 5236. At time t6 856 the SourceTerminal 100 having received the HLMSG signal from the DestinationTerminal 600 discontinues transmission of the MSD message. In a suitableexample, a retransmission is requested by the Destination Terminal 600via transmitting the start messages 802 again after a predeterminednumber of HLMSG signals have been sent by the Destination Terminal 600.In a suitable example, the predetermined number of HLMSG signals sent bythe Destination Terminal 600 is five. In a suitable example, theinteraction of FIG. 14A may contain an HLMSG signal comprising secondsync 893 and high layer message HLMSG 894, but not LLACK Signal (i.e.the HLMSG Signal is detected without a preceding LLACK signal).

FIG. 14B is another example interaction diagram of the synchronizationand data transmission sequences between the Source Terminal 100 and theDestination Terminal 600. This example follows the interactions of FIG.14A, with the exception that the HLMSG 894 is a high layer acknowledge(HLACK) message 894 a. In an exemplary use case, the Source Terminal 100may not detect the LLACK signal so continues transmitting the MSDmessage 812 multiple times (813, 814). At time t6 856 the SourceTerminal 100 having successfully received the HLACK signal from theDestination Terminal 600 discontinues transmission of the MSD message.The HLACK transmission serves to enhance the reliability of thecommunication between Source Terminal 100 and Destination Terminal 600as a redundant acknowledge to the LLACK message. For example, if theSource Terminal 100 is unable to detect the LLACK, it may detect theHLMSG resulting in an acknowledged data transmission without havingactually detected the LLACK. In an alternate embodiment, the HLMSG maybe a different message such as a call tear-down message.

FIG. 14C is another example interaction diagram of the synchronizationand data transmission sequences between the Source Terminal 100 and theDestination Terminal 600. This example follows the interactions of FIG.14A, with the exception that the HLMSG 894 is a high layer acknowledge(HLACK) message 894 a. In an exemplary use case, the Source Terminal 100detects the LLACK signal and at time t6 856 the Source Terminal 100having successfully received the LLACK signal from the DestinationTerminal 600 discontinues transmission of the MSD message.

FIG. 15 is another example interaction diagram of the synchronizationand data transmission sequences between the Source Terminal 100 and theDestination Terminal 600. In this case, the Uplink Transmission sequence810 is initiated by the Source Terminal 100 and the HLMSG 894 is a highlayer acknowledge (HLACK) message 894 a. To initiate the transmission,the Source Terminal 100 transmits an alternating sync 811 and “SEND”message 805 at time t0 850 b. At time t1 851 b the Destination Terminal600, having received the SEND message 805 from the Source Terminal 100,transmits an alternating first sync 801 and “Start” message 802. At timet2 852 b the Source Terminal 100, having received the “Start” message802 from the Destination Terminal 600, transmits a sync sequence 811followed by an MSD message 812 to the Destination Terminal 600. At timet3 853 b the Destination Terminal 600, having received the sync message811 from the Source Terminal 100, transmits an alternating first sync801 and “NACK” message 803 to the Source Terminal 100. At time t4 854,the Destination Terminal 600, having successfully received the MSDmessage, begins transmitting a low layer acknowledgement or “LLACKsignal” comprised of a first sync 801 and low layer acknowledgement“LLACK” message 804. At time t5 855, the Destination Terminal 600 beginstransmitting a high layer acknowledge or “HLACK signal” comprised of asecond sync 893 and high layer acknowledge message HLACK 894. At time t6856 the Source Terminal 100 having received the HLACK signal from theDestination Terminal 600 discontinues transmission of the MSD message.In alternate embodiments, the Source Terminal 100 may discontinuetransmission of the MSD message based on receiving the LLACK message, orboth LLACK and HLMSG messages.

FIG. 18C shows a flowchart for a method M100 of a Destination Terminal600 signaling to a Source Terminal 100 according to a firstconfiguration. Method M100 includes tasks T100, T101, T131, and T1212.Task T100 is shown in FIG. 18A and consists of subtasks that transmit astart signal T110, discontinues transmitting the start signal based onreceiving an indicator of a successful reception of the start signalT120, and transmits a negative acknowledgement (NACK) signal T130. TaskT101 is shown in FIG. 18B and consists of subtasks that discontinuetransmitting the NACK signal based on successful reception of a datamessage T111, and transmits a low layer acknowledgement (LLACK) signalT1211. Task T131 discontinues transmitting the LLACK signal when theDestination Terminal 600 receives an event on the uplink An uplink eventmay include a discontinued data message transmission from the SourceTerminal 100. An uplink event may alternatively include an indication ofa poor uplink channel condition. Task T1212 then transmits a high layeracknowledgement (HLACK) signal a predetermined number of times. Asuitable example of a predetermined number of HLACK transmissions isfive.

FIG. 18D shows a flowchart for a method M200 of a Destination Terminal600 signaling to a Source Terminal 100 according to a secondconfiguration. Method M200 includes tasks that transmit a start signalT110, discontinue transmitting the start signal based on receiving anindicator of a successful reception of the start signal T120, transmitsa negative acknowledgement (NACK) signal T130, and repeat the tasksT110, T120, and T130 a predetermined number of times if the DestinationTerminal 600 fails to successfully receive a source terminal datamessage. An example predetermined number of repeats may include fivetimes. If the Destination Terminal 600 successfully receives the sourceterminal data message before the predetermined number of repeats, MethodM200 continues with tasks that discontinue transmitting the NACK signalbased on successful reception of the source terminal data message T111,transmits an LLACK signal T1211, discontinues transmitting the LLACKsignal based on an uplink event T131, and transmits a high layeracknowledgement (HLACK) signal a predetermined number of times T1212.

FIG. 18E shows a flowchart for a method M300 of a Destination Terminal600 signaling to a Source Terminal 100 according to a thirdconfiguration. Method M300 includes tasks that transmit a start signalT110, discontinues transmitting the start signal based on receiving anindicator of a successful reception of the start signal T120, transmitsa negative acknowledgement (NACK) signal T130, discontinues transmittingthe NACK signal based on successful reception of a source terminal datamessage T111, transmits an LLACK signal T1211, discontinues transmittingthe LLACK signal if a predetermined number of LLACK signals have beentransmitted T132, and transmits a high layer acknowledgement (HLACK)signal a predetermined number of times T1212.

FIG. 19C shows a block diagram of an apparatus A10. Apparatus A10includes means F100, F101, F131, and F1212. Means F100 is shown in FIG.19A and consists of means for transmitting a start signal F110, meansfor discontinuing transmission of the start signal based on receiving anindication of a successful reception of the start signal F120, and meansfor transmitting a negative acknowledgement (NACK) signal F130. MeansF101 is shown in FIG. 19B and consists of means for discontinuingtransmission of the NACK signal based on successful reception of asource terminal data message F111, and means for transmitting a lowlayer acknowledgement (LLACK) signal F1211. Means F131 includes meansfor discontinuing transmission of the LLACK signal when the DestinationTerminal 600 receives an event on the uplink. Means F1212 includes meansfor transmitting a high layer acknowledgement (HLACK) signal apredetermined number of times.

FIG. 19D shows a block diagram of an apparatus A20. Apparatus A20includes means for transmitting a start signal F110, means fordiscontinuing transmission of the start signal based on receiving anindication of a successful reception of the start signal F120, means fortransmitting a negative acknowledgement (NACK) signal F130, means forrepeating means F110, F120, and F130 a predetermined number of times ifthe Destination Terminal 600 fails to successfully receive a sourceterminal data message, means for discontinuing transmission of the NACKsignal based on successful reception of the source terminal data messageF111, means for transmitting an LLACK signal F1211, means fordiscontinuing transmission of the LLACK signal when the DestinationTerminal 600 receives an event on the uplink F131, and means fortransmitting a high layer acknowledgement (HLACK) signal a predeterminednumber of times F1212.

FIG. 19E shows a block diagram of an apparatus A30. Apparatus A30includes means for transmitting a start signal F110, means fordiscontinuing transmission of the start signal based on receiving anindication of a successful reception of the start signal F120, means fortransmitting a negative acknowledgement (NACK) signal F130, means fordiscontinuing transmission of the NACK signal based on successfulreception of a source terminal data message F111, means for transmittinga low layer acknowledgement (LLACK) signal F1211, means fordiscontinuing transmitting the LLACK signal if a predetermined number ofLLACK signals have been transmitted, and means for transmitting a highlayer acknowledgement (HLACK) signal a predetermined number of timesF1212.

FIG. 20A shows a block diagram of an implementation of apparatus A10,A20, and A30 according to a first configuration. Start signal generator2010 generates a start signal as described herein with reference to taskT110 and is an implementation of means F110. NACK signal generator 2020generates a negative acknowledgement (NACK) signal as described hereinwith reference to task T130 and is an implementation of means F130.LLACK generator 2040 generates a low layer acknowledgement signal asdescribed herein with reference to task T1211 and is an implementationof means F1211. HLACK signal generator 2050 generates a high layeracknowledgement signal as described herein with reference to task T1212and is an implementation of means F1212. Successful reception of startsignal detector 4010 detects a signal that indicates a source terminalhas successfully received the transmitted start signal as describedherein with reference to task T120 and is an implementation of meansF120. Data message detector 4020 detects a source terminal data messageas described herein with reference to task T111 and is an implementationof means F111.

FIG. 20B shows a block diagram of an implementation of apparatus A10,A20, and A30 according to a second configuration. Processor 3000 is incommunication with Memory 3010, Transmitter 295 and Receiver 495. Memory3010 includes instructions which when executed by Processor 3000:generate start and NACK signals as described herein with reference totask T100 and implementation of means F100, discontinue NACK andgenerate LLACK signals as described herein with reference to task T101and implementation of means F101, discontinue transmitting LLACK signalbased on an uplink event as described herein with reference to task T131and implementation of means F131, repeat a sequence of tasks asdescribed herein with reference to task T133 and implementation F133,and transmit a HLACK signal a predetermined number of times as describedherein with reference to task T1212 and implementation of means F1212.One skilled in the art will recognize that a subset of tasks may existin Memory 3010, for example T100, T101, T131, and T1212 corresponding toM100.

FIG. 21A shows a block diagram for a method M400 of a Source Terminal100 signaling to a Destination Terminal 600 according to a generalconfiguration. Method M400 includes a task T210 that detects a requestsignal from the Destination Terminal 600, a task T220 that stores amessage identifier, a task T230 that transmits a sync signal based onthe detection of a request signal, a task T240 that transmits a userdata message, a task T2501 that detects an low layer acknowledgement(LLACK) signal, and a task T260 that discontinues transmitting the userdata message based on the detection of the LLACK signal. FIG. 21B showsa block diagram for a method M410 of a Source Terminal 100 signaling toa Destination Terminal 600. Method M410 includes a task T210 thatdetects a request signal from the Destination Terminal 600, a task T220that stores a message identifier, a task T230 that transmits a syncsignal based on the detection of a request signal, a task T240 thattransmits a user data message, a task T2502 that detects a high layeracknowledgement (HLACK) signal, and a task T261 that discontinuestransmitting the user data message based on the detection of the HLACKsignal. Task T2502 contains the subtasks shown in FIG. 21C whichincludes a task T25021 that regenerates a high layer applicationacknowledgement message, a task T25022 that forwards a high layerapplication acknowledgement message to a high layer application, and atask T25023 that receives an indication of successful receipt of a highlayer application acknowledgement message from a high layer application.Task T25021 contains the subtasks shown in FIG. 21D which includes atask T250211 that extracts a format field from a received transformedhigh layer acknowledgement (HLACK) message, a task T250212 that extractsa status field from a received transformed high layer acknowledgement(HLACK) message, a task T250213 that retrieves a stored messageidentifier, and a task T250214 that forms a high layer applicationacknowledgement message by combining the extracted fields and theretrieved message identifier. The formed high layer applicationacknowledgement message may alternatively contain a subset of extractedfields, for example only a status field and not a format field.

FIG. 22A shows a block diagram of an apparatus A40 according to ageneral configuration. Apparatus A40 includes a means for detecting arequest signal F210 from a Destination Terminal 600, a means for storinga message identifier F220, a means for transmitting a sync signal basedon the detection of a request signal F230, a means for transmitting auser data message F240, a means for detecting a low layeracknowledgement (LLACK) signal F2501, and a means for discontinuingtransmitting the user data message based on the detection of the LLACKsignal F260. FIG. 22B shows a block diagram of apparatus A41 andincludes a means for detecting a request signal F210 from a DestinationTerminal 600, a means for storing a message identifier F220, a means fortransmitting a sync signal based on the detection of a request signalF230, a means for transmitting a user data message F240, a means fordetecting a high layer acknowledgement (HLACK) signal F2502, and a meansfor discontinuing transmitting the user data message based on thedetection of the HLACK signal F261. FIG. 22C shows a block diagram ofmeans F2502 of apparatus A41 and includes means for regenerating a highlayer application acknowledgement message F25021, means for forwarding ahigh layer application acknowledgement message to a high layerapplication F25022, and means for receiving an indication of successfulreceipt of a high layer application acknowledgement message from a highlayer application F25023. FIG. 22D shows a block diagram of means F25021of apparatus A41 and includes means for extracting a format field from areceived transformed high layer acknowledgement message F250211, meansfor extracting a status field from a received transformed high layeracknowledgement message F250212, means for retrieving a locally storedmessage identifier F250213, and means for forming a high layerapplication acknowledgement message by combining the extracted fieldsand the retrieved message identifier F250214.

FIG. 23A shows a block diagram of an implementation of apparatus A40 andA41 according to a first configuration. Request signal detector 430detects a received request signal as described herein with reference totask T210 and is an implementation of means F210. Storage medium 340receives a message identifier as described herein with reference to taskT220. Sync signal generator 260 generates a sync signal as describedherein with reference to task T230 and is an implementation of meansF230. User data message generator 270 generates a user data message asdescribed herein with reference to task T240 and is an implementation ofmeans F240. High layer acknowledgement “HLACK” detector 442 detects ahigh layer acknowledgement signal as described herein with reference totask T2502 and is an implementation of means F2502. High layerapplication acknowledgement message regenerator 450 constructs a highlayer application acknowledgment message as described herein withreference to task T25021 and is an implementation of means F25021. FIG.24A shows a block diagram of an implementation of high layer applicationmessage regenerator 450 according to a first configuration. Statusextractor 451 extracts a status field as described herein with referenceto task T250212 and is an implementation of means F250212. Combiner 452combines at least an extracted status field with MSD identifier to formthe high layer application acknowledgement message and forwards themessage to a high layer application as described in task T250213 andT250214 and is an implementation of means F250213 and F250214. FIG. 24Bshows a block diagram of an implementation of high layer applicationmessage regenerator 450 according to a second configuration. The Highlayer application acknowledgement message regenerator 450 includes inaddition to Status extractor 451 and Combiner 452, a Format fieldextractor 453 to extract a format field as described herein withreference to task T250211 and is an implementation of means F250211. Inthe second configuration, Combiner 452 combines at least an extractedstatus field with an extracted format field and MSD identifier to formthe high layer application acknowledgement message.

FIG. 23B shows a block diagram of an implementation of apparatus A40 andA41 according to a second configuration. Processor 3020 is incommunication with Memory 3030, storage medium 340, Transmitter 295 andReceiver 495. Memory 3030 includes instructions which when executed byProcessor 3020: detects a request signal as described herein withreference to task T210 and implementation of means F210, stores amessage identifier as described herein with reference to task T220 andimplementation means F220, transmits a sync signal based on detection ofa request signal as described herein with reference to task T230 andimplementation means F230, transmits a user data message as describedherein with reference to task T240 and implementation means F240,detects a low layer acknowledgement signal as described herein withreference to task T2501 and implementation means F2501, detects a highlayer acknowledgement signal as described herein with reference to taskT2502 and implementation means F2502, discontinues transmission of theuser data message based on detection of the low layer acknowledgementsignal as described herein with reference to task T260 andimplementation means F260, and discontinues transmission of the userdata message based on detection of the high layer acknowledgement signalas described herein with reference to task T261 and implementation meansF261. One skilled in the art will recognize that a subset of tasks mayexist in Memory 3030.

FIG. 25 is a first example use case of the system and methods disclosedherein. The diagram represents a typical example of the emergency call(eCall) system. A vehicle incident 950 is shown as an accident betweentwo vehicles. Other suitable examples for vehicle incident 950 includemultiple vehicle accident, single vehicle accident, single vehicle flattire, single vehicle engine malfunction or other situations where thevehicle malfunctions or the user is in need of assistance. TheIn-Vehicle System (IVS) 951 is located in one or more of the vehiclesinvolved in the vehicle incident 950 or may be located on the userhimself The In-Vehicle System 951 may be comprised of the sourceterminal 100 described herein. The In-Vehicle System 951 communicatesover a wireless channel which may be comprised of an uplinkcommunications channel 501 and downlink communications channel 502. Arequest for data transmission may be received by the In-Vehicle Systemthrough the communications channel or may be automatic or manuallygenerated at the In-Vehicle System. A wireless tower 955 receives thetransmission from the In-Vehicle System 951 and interfaces to a wirelinenetwork comprised of a wireline uplink 962 and wireline downlink 961. Asuitable example of a wireless tower 955 is a cellular telephonecommunications tower comprised of antennas, transceivers, and backhaulequipment, all well-known in the art, for interfacing to the wirelessuplink 501 and downlink 502. The wireline network interfaces to a PublicSafety Answering Point (PSAP) 960, where emergency informationtransmitted by the In-Vehicle System 951 may be received and control anddata transmitted. The Public Safety Answering Point 960 may be comprisedof the destination terminal 600 described herein. The communicationbetween the In-Vehicle System 951 and the Public Safety Answering Point960 may be accomplished using the interaction diagrams described herein.Other suitable examples for vehicle incident 950 may also includevehicle inspection, servicing, diagnostic or other situations wherein-band data transfer from a vehicle may occur. In this case the PublicSafety Answering Point (PSAP) 960 may be replaced by a destinationterminal server.

The methods and apparatus disclosed herein may be applied generally inany transceiving and/or audio sensing application, especially mobile orotherwise portable instances of such applications. For example, therange of configurations disclosed herein includes communications devicesthat reside in a wireless telephony communication system configured toemploy a code-division multiple-access (CDMA) over-the-air interface.Nevertheless, it would be understood by those skilled in the art that amethod and apparatus having features as described herein may reside inany of the various communication systems employing a wide range oftechnologies known to those of skill in the art, such as systemsemploying Voice over IP (VoIP) over wired and/or wireless (e.g., CDMA,TDMA, FDMA, and/or TD-SCDMA) transmission channels.

The foregoing presentation of the described configurations is providedto enable any person skilled in the art to make or use the methods andother structures disclosed herein. The flowcharts, block diagrams, andother structures shown and described herein are examples only, and othervariants of these structures are also within the scope of thedisclosure. Various modifications to these configurations are possible,and the generic principles presented herein may be applied to otherconfigurations as well. Thus, the present disclosure is not intended tobe limited to the configurations shown above but rather is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed in any fashion herein, including in the attachedclaims as filed, which form a part of the original disclosure.

Those of skill in the art will understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, and symbols that may be referenced throughout the abovedescription may be represented by voltages, currents, electromagneticwaves, magnetic fields or particles, optical fields or particles, or anycombination thereof.

The various elements of an implementation of an apparatus as disclosedherein may be embodied in any combination of hardware, software, and/orfirmware that is deemed suitable for the intended application. Forexample, such elements may be fabricated as electronic and/or opticaldevices residing, for example, on the same chip or among two or morechips in a chipset. One example of such a device is a fixed orprogrammable array of logic elements, such as transistors or logicgates, and any of these elements may be implemented as one or more sucharrays. Any two or more, or even all, of these elements may beimplemented within the same array or arrays. Such an array or arrays maybe implemented within one or more chips (for example, within a chipsetincluding two or more chips).

One or more elements of the various implementations of the apparatusdisclosed herein may also be implemented in whole or in part as one ormore sets of instructions arranged to execute on one or more fixed orprogrammable arrays of logic elements, such as microprocessors, embeddedprocessors, IP cores, digital signal processors, FPGAs(field-programmable gate arrays), ASSPs (application-specific standardproducts), and ASICs (application-specific integrated circuits). Any ofthe various elements of an implementation of an apparatus as disclosedherein may also be embodied as one or more computers (e.g., machinesincluding one or more arrays programmed to execute one or more sets orsequences of instructions, also called “processors”), and any two ormore, or even all, of these elements may be implemented within the samesuch computer or computers.

A processor or other means for processing as disclosed herein may befabricated as one or more electronic and/or optical devices residing,for example, on the same chip or among two or more chips in a chipset.One example of such a device is a fixed or programmable array of logicelements, such as transistors or logic gates, and any of these elementsmay be implemented as one or more such arrays. Such an array or arraysmay be implemented within one or more chips (for example, within achipset including two or more chips). Examples of such arrays includefixed or programmable arrays of logic elements, such as microprocessors,embedded processors, IP cores, DSPs, FPGAs, ASSPs, and ASICs. Aprocessor or other means for processing as disclosed herein may also beembodied as one or more computers (e.g., machines including one or morearrays programmed to execute one or more sets or sequences ofinstructions) or other processors. It is possible for a processor asdescribed herein to be used to perform tasks or execute other sets ofinstructions that are not directly related to a high protocol messagingprocedure, such as a task relating to another operation of a device orsystem in which the processor is embedded. It is also possible for partof a method as disclosed herein to be performed by a first processor andfor another part of the method to be performed under the control of oneor more other processors.

Those of skill will appreciate that the various illustrative modules,logical blocks, circuits, and tests and other operations described inconnection with the configurations disclosed herein may be implementedas electronic hardware, computer software, or combinations of both. Suchmodules, logical blocks, circuits, and operations may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an ASIC or ASSP, an FPGA or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to produce the configuration as disclosedherein. For example, such a configuration may be implemented at least inpart as a hard-wired circuit, as a circuit configuration fabricated intoan application-specific integrated circuit, or as a firmware programloaded into non-volatile storage or a software program loaded from orinto a data storage medium as machine-readable code, such code beinginstructions executable by an array of logic elements such as a generalpurpose processor or other digital signal processing unit. A generalpurpose processor may be a microprocessor, but in the alternative, theprocessor may be any conventional processor, controller,microcontroller, or state machine. A processor may also be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. A software module may reside in RAM (random-accessmemory), ROM (read-only memory), nonvolatile RAM (NVRAM) such as flashRAM, erasable programmable ROM (EPROM), electrically erasableprogrammable ROM (EEPROM), registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anillustrative storage medium is coupled to the processor such theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

An illustrative controlling apparatus is coupled to the controlledsystem. The controlled system contains modules for instructing thecontrolled system to perform operations described in connection with theconfigurations disclosed herein. The modules may be implemented asinstruction modules that are encoded into the controlling apparatus. Acontrolling apparatus may be RAM (random-access memory), ROM (read-onlymemory), nonvolatile RAM (NVRAM) such as flash RAM, erasableprogrammable ROM (EPROM), electrically erasable programmable ROM(EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any otherform of storage medium known in the art.

It is noted that the various methods disclosed herein may be performedby an array of logic elements such as a processor, and that the variouselements of an apparatus as described herein may be implemented asmodules designed to execute on such an array. As used herein, the term“module” or “sub-module” can refer to any method, apparatus, device,unit or computer-readable data storage medium that includes computerinstructions (e.g., logical expressions) in software, hardware orfirmware form. It is to be understood that multiple modules or systemscan be combined into one module or system and one module or system canbe separated into multiple modules or systems to perform the samefunctions. When implemented in software or other computer-executableinstructions, the elements of a process are essentially the codesegments to perform the related tasks, such as with routines, programs,objects, components, data structures, and the like. The term “software”should be understood to include source code, assembly language code,machine code, binary code, firmware, macrocode, microcode, any one ormore sets or sequences of instructions executable by an array of logicelements, and any combination of such examples. The program or codesegments can be stored in a processor readable medium or transmitted bya computer data signal embodied in a carrier wave over a transmissionmedium or communication link.

The implementations of methods, schemes, and techniques disclosed hereinmay also be tangibly embodied (for example, in one or morecomputer-readable media as listed herein) as one or more sets ofinstructions readable and/or executable by a machine including an arrayof logic elements (e.g., a processor, microprocessor, microcontroller,or other finite state machine). The term “computer-readable medium” mayinclude any medium that can store or transfer information, includingvolatile, nonvolatile, removable and non-removable media. Examples of acomputer-readable medium include an electronic circuit, a semiconductormemory device, a ROM, a flash memory, an erasable ROM (EROM), a floppydiskette or other magnetic storage, a CD-ROM/DVD or other opticalstorage, a hard disk, a fiber optic medium, a radio frequency (RF) link,or any other medium which can be used to store the desired informationand which can be accessed. The computer data signal may include anysignal that can propagate over a transmission medium such as electronicnetwork channels, optical fibers, air, electromagnetic, RF links, etc.The code segments may be downloaded via computer networks such as theInternet or an intranet. In any case, the scope of the presentdisclosure should not be construed as limited by such embodiments.

Each of the tasks of the methods described herein may be embodieddirectly in hardware, in a software module executed by a processor, orin a combination of the two. In a typical application of animplementation of a method as disclosed herein, an array of logicelements (e.g., logic gates) is configured to perform one, more thanone, or even all of the various tasks of the method. One or more(possibly all) of the tasks may also be implemented as code (e.g., oneor more sets of instructions), embodied in a computer program product(e.g., one or more data storage media such as disks, flash or othernonvolatile memory cards, semiconductor memory chips, etc.), that isreadable and/or executable by a machine (e.g., a computer) including anarray of logic elements (e.g., a processor, microprocessor,microcontroller, or other finite state machine). The tasks of animplementation of a method as disclosed herein may also be performed bymore than one such array or machine. In these or other implementations,the tasks may be performed within a device for wireless communicationssuch as a cellular telephone or other device having such communicationscapability. Such a device may be configured to communicate withcircuit-switched and/or packet-switched networks (e.g., using one ormore protocols such as VoIP).

It is expressly disclosed that the various methods disclosed herein maybe performed by a portable communications device such as a handset,headset, or portable digital assistant (PDA), and that the variousapparatus described herein may be included within such a device. Atypical real-time (e.g., online) application is a telephone conversationconducted using such a mobile device.

In one or more exemplary embodiments, the operations described hereinmay be implemented in hardware, software, firmware, or any combinationthereof If implemented in software, such operations may be stored on ortransmitted over a computer-readable medium as one or more instructionsor code. The term “computer-readable media” includes both computerstorage media and communication media, including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise an array of storage elements, such as semiconductormemory (which may include without limitation dynamic or static RAM, ROM,EEPROM, and/or flash RAM), or ferroelectric, magnetoresistive, ovonic,polymeric, or phase-change memory; CD-ROM or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium that can be used to carry or store desired program code in theform of instructions or data structures and that can be accessed by acomputer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technology suchas infrared, radio, and/or microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technology such as infrared,radio, and/or microwave are included in the definition of medium. Diskand disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and Blu-rayDisc™ (Blu-Ray Disc Association, Universal City, Calif.), where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

1. A method of acknowledging a source terminal data message from adestination terminal in an in-band communication system, the methodcomprising: transmitting a low layer acknowledgement (LLACK) signal,wherein the LLACK signal is comprised of a first synchronizationsequence followed by a LLACK message; and transmitting a high layerapplication (HLMSG) signal, wherein the HLMSG signal is comprised of asecond synchronization sequence followed by a transformed HLMSG message.2. The method of claim 1, wherein the transformed HLMSG message is ahigh layer acknowledgement (HLACK) message comprised of at least amessage status identifier.
 3. The method of claim 2, wherein thetransformed HLMSG further comprises a format identifier.
 4. The methodof claim 1, further comprising discontinuing transmission of the LLACKsignal upon detection of an uplink event.
 5. The method of claim 1,further comprising the steps of: transmitting a start signal from thedestination terminal, whereby the source terminal is constrained torespond in a first predetermined manner; discontinuing transmission ofthe start signal upon detection of a first received signal, wherein thefirst received signal indicates a successful reception of the startsignal from the source terminal; transmitting a negative acknowledgement(NACK) signal from the destination terminal, whereby the source terminalis constrained to respond in a second predetermined manner; anddiscontinuing transmission of the NACK signal upon successful receptionof the source terminal data message.
 6. The method of claim 5 whereinthe start signal is comprised of a first synchronization signal followedby a start message.
 7. The method of claim 5 wherein the NACK signal iscomprised of a first synchronization signal followed by a NACK message.8. The method of claim 5 wherein the successfully received sourceterminal data message is the data message verified by a cyclicredundancy check.
 9. The method of claim 5 further comprising repeatingthe steps based on the transmission of a predetermined number of theNACK signals without successful reception of the source terminal datamessage.
 10. The method of claim 4, wherein the uplink event is adiscontinued source terminal data message transmission.
 11. The methodof claim 4 wherein the uplink event is the transmission of apredetermined number of the LLACK signals.
 12. An apparatus comprising:a transmitter configured to transmit signals from a destinationterminal; a receiver configured to receive signals from a sourceterminal at the destination terminal; a start signal generator coupledto the transmitter and configured to generate a start signal; a NACKsignal generator coupled to the transmitter and configured to generate aNACK signal; a data message detector coupled to the receiver andconfigured to detect a source terminal data message; a LLACK signalgenerator coupled to the transmitter and configured to generate a firstsynchronization sequence followed by an LLACK message; and a HLACKsignal generator coupled to the transmitter and configured to generate asecond synchronization sequence followed by a transformed HLACK message.13. The apparatus of claim 12 wherein the start signal is comprised of afirst synchronization signal followed by a start message.
 14. Theapparatus of claim 12 wherein the NACK signal is comprised of a firstsynchronization signal followed by a NACK message.
 15. An apparatuscomprising: a processor; memory in electronic communication with theprocessor; and instructions stored in the memory, the instructions beingcapable of executing the steps of: transmitting a low layeracknowledgement (LLACK) signal, wherein the LLACK signal is comprised ofa first synchronization sequence followed by a LLACK message; andtransmitting a high layer application (HLMSG) signal, wherein the HLMSGsignal is comprised of a second synchronization sequence followed by atransformed HLMSG message, wherein the transformed HLMSG message is ahigh layer acknowledgement (HLACK) message.
 16. The apparatus of claim15 wherein the memory further comprises instructions, the instructionsbeing executable to discontinue transmission of the LLACK signal upondetection of an uplink event.
 17. The apparatus of claim 15 wherein thememory further comprises instructions, the instructions being capable ofexecuting the steps of: transmitting a start signal from the destinationterminal; discontinuing transmission of the start signal upon detectionof a first received signal, wherein the first received signal indicatesa successful reception of the start signal from a source terminal;transmitting a NACK signal from the destination terminal; anddiscontinuing transmission of the NACK signal upon successful receptionof a source terminal data message.
 18. The apparatus of claim 17 whereinthe start signal is comprised of a first synchronization signal followedby a start message.
 19. The apparatus of claim 17 wherein the NACKsignal is comprised of a first synchronization signal followed by a NACKmessage.
 20. The apparatus of claim 17 wherein the memory furthercomprises instructions, the instructions being executable to repeat thesteps based on the transmission of a predetermined number of the NACKsignals without successful reception of the source terminal datamessage.
 21. The apparatus of claim 16 wherein the uplink event is adiscontinued source terminal data message transmission.
 22. Theapparatus of claim 16 wherein the uplink event is the transmission of apredetermined number of the LLACK signals.
 23. An apparatus foracknowledging a source terminal data message from a destination terminalin an in-band communication system comprising: means for transmitting alow layer acknowledgement (LLACK) signal, wherein the LLACK signal iscomprised of a first synchronization sequence followed by a LLACKmessage; and means for transmitting a high layer application (HLMSG)signal, wherein the HLMSG signal is comprised of a secondsynchronization sequence followed by a transformed HLMSG message,wherein the transformed HLMSG message is a high layer acknowledgement(HLACK) message.
 24. The method of claim 23, further comprising meansfor discontinuing transmission of the LLACK signal upon detection of anuplink event.
 25. The apparatus of claim 23 further comprising: meansfor transmitting a start signal from the destination terminal; means fordiscontinuing transmission of the start signal upon detection of a firstreceived signal, wherein the first received signal indicates asuccessful reception of the start signal from a source terminal; meansfor transmitting a NACK signal from the destination terminal, wherebythe source terminal is constrained to respond in a first predeterminedmanner; and means for discontinuing transmission of the NACK signal upondetection of a successfully received source terminal data message. 26.The apparatus of claim 25 wherein the start signal is comprised of afirst synchronization signal followed by a start message.
 27. Theapparatus of claim 25 wherein the NACK signal is comprised of a firstsynchronization signal followed by a NACK message.
 28. A processorreadable medium for acknowledging a source terminal data message from adestination terminal in an in-band communication system, comprisinginstructions for: transmitting a start signal from the destinationterminal, whereby the source terminal is constrained to respond in afirst predetermined manner; discontinuing transmission of the startsignal upon detection of a first received signal, wherein the firstreceived signal indicates a successful reception of the start signalfrom the source terminal; transmitting a negative acknowledgement (NACK)signal from the destination terminal, whereby the source terminal isconstrained to respond in a second predetermined manner; discontinuingtransmission of the NACK signal upon successful reception of the sourceterminal data message; transmitting a low layer acknowledgement (LLACK)signal, wherein the LLACK signal is comprised of a first synchronizationsequence followed by a LLACK message; transmitting a high layerapplication (HLMSG) signal, wherein the HLMSG signal is comprised of asecond synchronization sequence followed by a transformed HLMSG message,wherein the transformed HLMSG message is a high layer acknowledgement(HLACK) message; and discontinuing transmission of the LLACK signal upondetection of an uplink event.